For example, an underpants-type disposable diaper includes an outer body having a front body part and a back body part, and an inner body that includes an absorber and is fixed to the inner surface of the outer body. The front body part and the back body part of the outer body are joined at the both sides to form a waist opening and a pair of right and left leg openings.
In the underpants-type disposable diaper, elongated resilient and elastic members such as rubber threads are fixed in an extended state at several sections of the outer body along a circumferential direction to form a stretchable structure around the waist portion to enhance the fit to the human body. In particular, diapers including waist-edge resilient and elastic members at the edge portion of the waist opening along the width direction and waist-lower portion resilient and elastic members closer to the crotch portion than the waist-edge resilient and elastic members along the width direction, are widely used due to their relatively good fit to the human body.
Meanwhile, a tape-type disposable diaper has a crotch portion, a ventral-side portion extended to the front side of the crotch portion, a back-side portion extended to the back side of the crotch portion, an absorber provided in an area including the crotch portion, fastening tapes protruding from the both sides of the back portion, and target tapes positioned on the outer surface of the ventral-side portion, to which the fastening tapes are to be fastened. To put the diaper on the wearer's body, the fastening tapes are turned from the both sides of the waist toward the outer surface of the ventral-side portion and are fastened to the target tapes. The tape-type disposable diapers are widely used for infants and for recipients of care (adults) as well. In general, the tape-type disposable diapers are inferior in a fit around the waist to the underpants-type disposable diapers. To improve this, elongated resilient and elastic members such as rubber threads are fixed in the extended state to the back side portion and the fastening tapes along the width direction to form a stretchable structure around the waist portion.
In addition, as an improvement of these stretchable structures, there have been proposed stretchable structures in which two sheet materials are intermittently joined in a stretching direction and a longitudinal direction orthogonal to the stretching direction to form a large number of sheet joined sections, and a plurality of stretchable elongated resilient and elastic members is arranged independent from the two sheet materials so as not to pass through the sheet joined sections (so as to pass through the non-joined sections) between the sheet materials (refer to Patent Documents 1 and 2. These stretchable structures will be hereinafter also referred to as vertical intermittent joined form). According to the related art, the vertically aligned the sheet joined sections form vertically continuous grooves, and the sections between the grooves form large pleats that swell to the same degree on the both front and back sides. The grooves improve air permeability and the pleats produce excellent fluffy.
For improvement in appearance, there has also been proposed a stretchable structure in which the fixed portion of resilient and elastic members is frilled on the outside (refer to Patent Document 4).